Anas al-Abdah, president of the opposition Syrian Coalition, told reporters in Istanbul, Turkey, that the victory -- which saw rebel fighters defeat the might of the Syrian regime along with Iranian, Hezbollah and Russian military power -- was "almost a miracle."

"To be able to break these forces and to break the siege and now move into a stage where we are talking seriously about liberating the city I think is miraculous in every possible way," he said Monday.

Little relief yet

The victory has opened a fragile corridor between previously encircled opposition-held territory in the east of the city and the lands controlled by their allies to the west, raising hopes that relief for besieged rebel-held neighborhoods will be on the way.

But only a trickle of aid has reached opposition-held eastern neighborhoods, where about 250,000 people are suffering acute shortages of food, fuel and medicine, so far, sources say. Aid agencies say they have humanitarian aid standing by and ready to be delivered, but the route, which remains under heavy bombardment, is too dangerous for convoys to enter.

Al-Abdah said emergency plans were in place to work with local councils in eastern Aleppo to deliver basic services to the area, which the United Nations has warned faced a humanitarian disaster under the government siege.

Residents have been living under siege since they were gradually encircled by Syrian government troops and their allies in the spring, with the final supply lines into the enclave cut off last month.

Syrian state news agency SANA says that the rebels have not broken the siege. The agency reports that government troops had inflicted "heavy losses" on rebel groups in the fighting raging in the south and southwest of the city.

Fighters from Jabhat Fateh al Sham -- formerly the al Nusra Front -- advance through a government military complex in Aleppo Saturday.

Intense airstrikes as regime fights back

The area remains the scene of intense fighting -- some of the most ferocious in the conflict's five-year history -- with waves of heavy regime airstrikes and rocket attacks launched in response, as the Syrian government attempts to win back the territory.

The UK-based monitoring group, the Syrian Observatory for Human Rights, said there were heavy air raids on eastern Aleppo in the early hours of Monday, while rebel forces shelled government held areas.

The rebel advance into Ramouseh -- where rebels have captured a government military complex -- has now raised questions about the security of supply lines into government-held western Aleppo.

State-run news agency SANA and the Syrian Observatory for Human Rights both reported Monday that trucks of food and gas had been brought into government-held western Aleppo.

Aleppo, Syria's pre-war economic hub, has been divided since 2012 between a government-held western half and eastern neighborhoods under rebel control.

Fighters from Jabhat Fateh al Sham -- formerly the al Nusra Front -- sit in a trench after capturing a key government position in Aleppo.

Radical Islamists lead charge

The rebel offensive has been led by Jabhat Fateh al Sham, a radical Islamist group that up until two weeks ago was known as the al Nusra Front.

The group rebranded itself by declaring it was breaking its long-standing ties with al Qaeda to build closer alliances with other jihadist and rebel groups in Syria. The group has employed suicide bombers in its assault on regime positions in the recent fighting in Aleppo.

Jaysh al Fateh -- the rebel alliance comprised of Islamist groups as well as so-called moderates -- released a statement Sunday declaring that its fighters would continue battling to capture the entire city, and vowing to protect residents.

Speaking in Istanbul Monday, opposition leader al-Abdah praised the rebel fighters and said Aleppo residents had nothing to fear from the rebels, "because the main aspect of our work in Aleppo is to liberate them."

He also called on Syrian Army soldiers to defect to the rebels. "This could be the last chance for them to side with the people rather than the dictator," he said.

Addressing rebel fighters across the country, he said the key to defeating government forces was uniting against the regime.

"I think this is a message to all other revolutionary forces across Syria ... the secret recipe for winning over the regime is to unite both militarily and politically."

Use of phosphorus bombs alleged in Idlib

Al-Abdah also accused the Syrian regime and its Russian backers of war crimes after reports that phosphorus bombs were dropped on Idlib city in northern Syria last night.

"Very clearly... what's happening there is a war crime by all means," he said.

The Idlib Civil Defense -- a volunteer search-and-rescue group known as the White Helmets -- said that four phosphorus bombs were dropped and images of the purported attack were circulated on social media.

Russian state news agency Sputnik reported on strikes "by what appear to be incendiary bombs" in Idlib, "in a bid to root out al-Nusra rebels and recapture the balance in the fight to stabilize Syria."

Phosphorus bombs, which can cause serious chemical burns, are controversial but not banned by any treaty.

ISIS close to losing crucial hub

Elsewhere in northern Syria, US-backed militias have nearly captured from ISIS the city of Manbij, some 50 miles (80 kilometers) northeast of Aleppo.

The group said Monday it was offering ISIS fighters safe passage out of the city in exchange for releasing civilians they are holding as human shields.

U.S.-backed Kurdish and Arab fighters prepare a rocket-launcher as they advance into Manbij last June.

The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab militias, has taken about 90% of the strategic city from the Sunni terror group, an SDF spokesman, Sherfan Darwish, told CNN Sunday. Battles in the city are ongoing, he said.

The SDF's Manbij Military Council released a statement Monday saying it was prepared to give elements of ISIS who remained in the city the opportunity to leave "on the condition that they release all the civilians they are holding and all their prisoners."

According to the statement, ISIS took civilians prisoners to use as human shields as they were pushed to the city's northern districts, reportedly executing anyone who did not follow their orders.

The SDF has been fighting ISIS in the city for more than two months.

Manbij, about 25 miles (40 kilometers) from the Turkish border, is a key possession for ISIS and the principal hub on its supply route between the Turkish border and Raqqa, the capital of its self-declared caliphate.

The city has proven instrumental in allowing ISIS to smuggle weapons and foreign fighters in and out of its so-called caliphate.